I asked why humanity took so long to do anything at the start, and the Internet gave me its thoughts. Here is my expanded list of hypotheses, summarizing from comments on the post, here, and here.

Inventing is harder than it looks

1. Inventions are usually more ingenious than they seem. Relatedly, reality has a lot of detail.
2. There are lots of apparent paths: without hindsight, you have to waste a lot of time on dead ends.
3. People are not as inventive as they imagine. For instance, I haven’t actually invented anything – why do I even imagine I could invent rope?
4. Posing the question is a large part of the work. If you have never seen rope, it actually doesn’t occur to you that rope would come in handy, or to ask yourself how to make some.
5. Animals (including humans) mostly think by intuitively recognizing over time what is promising and not among affordances they have, and reading what common observations imply. New affordances generally only appear by some outside force e.g. accidentally. To invent a thing, you have to somehow have an affordance to make it even though you have never seen it. And in retrospect it seems so obvious because now you do have the affordance.

People fifty thousand years ago were not really behaviorally modern

1. People’s brains were actually biologically less functional fifty thousand years ago.
2. Having concepts in general is a big deal. You need a foundation of knowledge and mental models to come up with more of them.
3. We lacked a small number of unimaginably basic concepts that it is hard to even imagine not having now. For instance ‘abstraction’, or ‘changing the world around you to make it better’.
4. Having external thinking tools is a big deal. Modern ‘human intelligence’ relies a lot on things like writing and collected data, that aren’t in anyone’s brain.
5. The entire mental landscapes of early people was very different, as Julian Jaynes suggests. In particular, they lacked self awareness and the ability to have original thought rather than just repeating whatever they usually repeat.

Prerequisites

1. Often A isn’t useful without B, and B isn’t useful without A. For instance, A is chariots and B is roads.
2. A isn’t useful without lots of other things, which don’t depend on A, but take longer to accrue than you imagine.
3. Lots of ways to solve problems don’t lead to great things in the long run. ‘Crude hacks’ get you most of the way there, reducing the value of great inventions.

Nobody can do much at all

1. People in general are stupid in all domains, even now. Everything is always mysteriously a thousand times harder than you might think.
2. Have I tried even making rope from scratch? Let alone inventing it?

People were really busy

1. Poverty traps. Inventing only pays off long term, so for anyone to do it you need spare wealth and maybe institutions for capital to fund invention.
2. People are just really busy doing and thinking about other things. Like mating and dancing and eating and so on.

Communication and records

1. The early humans did have those things, we just don’t have good records. Which is not surprising, because our records of those times are clearly very lacking.
2. Things got invented a lot, but communication wasn’t good/common enough to spread them. For instance because tribes were small and didn’t interact that much).

Social costs

1. Technology might have been seen as a sign of weakness or laziness
2. Making technology might make you stand out rather than fit in
3. Productivity shames your peers and invites more work from you
4. Inventions are sometimes against received wisdom

Population

1. There were very few people in the past, so the total thinking occurring between 50k and 28k years ago was less than in the last hundred years.

Value

1. We didn’t invent things until they became relevant at all, and most of these things aren’t relevant to a hunter-gatherer.
2. Innovation is risky: if you try a new thing, you might die.

Orders of invention

1. First order inventions are those where the raw materials are in your immediate surroundings, and they don’t require huge amounts of skill. My intuition is mostly that first order inventions should have been faster. But maybe we did get very good at first order ones quickly, but it is hard to move to higher orders.
2. You need a full-time craftsman to make most basic things to a quality where they are worth having, and we couldn’t afford full-time craftsmen for a very long time.
3. Each new layer requires the last layer of innovation be common enough that it is available everywhere, for the next person to use.